Method and apparatus for balancing pneumatic tire and support

ABSTRACT

The method of substantially dynamically and statically balancing a pneumatic tire and its support wheel or rim which includes the steps of 1. MEASURING THE DISTANCE THAT SIDEWALL AND/OR TREAD PORTIONS OF THE TIRE EXTEND AXIALLY FROM THE SUPPORT TO DETERMINE ANY DIFFERENCES IN THESE DISTANCES. 2. COMPENSATING FOR ANY DIFFERENCES IN THE DISTANCES BY SECURING A COMPENSATING WEIGHT ON THE SUPPORT DIAMETRICALLY OPPOSITE TO THE GREATEST DIFFERENCE DISTANCE TO THEREBY BALANCE STATICALLY WITH A COMPENSATING WEIGHT, POSITIONED ON THE OPPOSITE SIDE OF THE TIRE SUPPORT IN ALIGNMENT IN AN AXIAL DIRECTION. The apparatus for substantially dynamically and statically balancing a pneumatic tire and its support wheel or rim includes a plurality of radically extending arms, roller means on certain of the arms and adapted to engage with the tire support to rotatably support the hub and arms thereon, and gage means mounted on at least one arm to measure the distance that sidewall and/or tread portions of the tire extend axially from the support to determine any difference in these distances.

United States Patent [1 1 Skidmore Sept. 25, 1973 4] METHOD ANDAPPARATUS FOR BALANCING PNEUMATIC TIRE AND SUPPORT [76] Inventor: FrankO. Skidmore, 2513 Third St.,

Cuyahoga Falls, Ohio 44221 [22] Filed: July 14, 1971 [2]] Appl. No.:162,552

Related US. Application Data [63] Continuation-impart of Ser. No.667,573, Sept. 13, 1967, abandoned, and a continuation-in-part of Ser.No. 761,360, June 26, 1968, Pat. No. 3,595,068.

[52] U.S. Cl. 73/66, 73/487 [51] lnt. Cl. G0lm 1/12 [58] Field of Search73/66, 480, 481, 73/487 I [56] References Cited 7 UNITED STATES PATENTS3,595,068 7/1971 Skidmore 73/66 3,177,725 4/1965 .lohnson..... 2,378,2376/1945 Morris 73/676 Primary Examiner.lames J. Gill Anomey-Albert H.Oldham et a1.

OUTPUT SIGNAL [57] ABSTRACT The method of substantially dynamically andstatically balancing a pneumatic tire and its support wheel or rim whichincludes the steps of l. measuring the distance that sidewall and/ortread portions of the tire extend axially from the support to determineany differences in these distances. 2. compensating for any differencesin the distances by securing a compensating weight on the supportdiametrically opposite to the greatest difference distance to therebybalance statically with a compensating weight, positioned on theopposite side of the tire support in alignment in an axial direction.

The apparatus for substantially dynamically and I statically balancing apneumatic tire and its support wheel or rim includes a plurality ofradically extending arms, roller means on certain of the arms andadapted to engage with the tire support to rotatably support the hub andarms thereon, and gage means mounted on at least one arm to measure thedistance that sidewall and/or tread portions of the tire extend axiallyfrom the support to determine any difference in these distances.

1 Claim, 8 Drawing Figures RADIATION POWER SOURCE PATENTED 3E? OUTPUTSIGNAL sumanra INVENTOR FRANK O. SKIDMORE ATTORNEYS METHOD AND APPARATUSFOR BALANCING PNEUMATIC TIRE AND SUPPORT This application is acontinuation-in-part of my appli cation Ser. No. 667,573, filed Sept.13, 1967, now abandoned and my application Ser. No. 761,360, filed June26, 1968, now US. Pat. No. 3,595,068, issued July 27, 1971.

It is the object of .the invention to provide relatively inexpensiveapparatus and methods for quickly, with good accuracy, balancing apneumatic tire and its wheel or rim support both dynamically andstatically. Present bubble-balancing or spindle type balancing equipmentcan only achieve static balance, not dynamic.

In the drawings:

FIG. 1 is a diagrammatic cross-sectional view of a tire and its supportshowingareas of dynamic and static unbalance and formulas for effectingbalance,

FIG. 2 is a perspective view of one embodiment of apparatus of theinvention;

FIG. 3 is an enlarged fragmentary view of a tire support with anassociated roller means of FIG. 2;

FIG. 4 is an enlarged fragmentary cross-sectional view of a gage meansfrom FIG. 2; and

FIG. 5 is an enlarged broken away cross-sectional view of a modifiedembodiment of the invention;

FIG. 6 is a plan schematic of the tool of FIG. 5 which illustrates someother attachments to the basic tool;

FIG. 7 is a schematic illustration showing how equal balance is achievedin the whole tire, rim, combination using the apparatus and method ofthe invention; and

FIG. 8 is a schematic illustration of a radiation detector fordetermining laterally displaced heavy areas for factory marking, forexample.

The schematic showing of FIG. 1 includes a penumatic tire 10 carried ona support wheel or rim 12. The tire I0 is shown with an exaggeratedstatically out-ofbalance tread area w at a distance r from the axis ofrotation 14. The tire 10 is also shown with an exaggerated dynamicallyout-of-balance sidewall area W at a distance of R from the axis ofrotation 14. The sidewall area W is at a distance or moment arm A fromthe center plane 16 of the tire support 12.

When the tire 10 of FIG. 1 is spun on axis 14 the sidewall unbalancearea W throws the tire into a dynamically unbalanced condition tendingto twist the center weight w in FIG. 1, as this also follows the formulaabove.

The amount of weight W to effect counter-balance is a function or factorof the distance of the axially parallel offsetting of area W. In a greatmany cases area W is caused not by faulty sidewall construction of thetire, but because the tire is seated on the rim in a cockedrelationship. In other words, the plane of the tire does not coincidewith the plane of the rim. This cocked relationship causes sidewall andtread offset and misalignment with the rim, and consequent dynamicunbalance. If the distance of the sidewall offset is one-half inch alarger weight W will have to be used than if the axial offset is onlyone-eighth inch. In any event, the amount of the axial offset ismeasured (as hereinafter described) and a table is established equatingeach difference in offset distance to a given weight for selected tiresizes, testing bearing loads dynamically to insure best dynamic balance,and this table, or a series thereof, is supplied with the apparatus tothe customer. The computation of the .table does not comprise a part ofthe invention, but depends on the size and characteristics of the tirebeing balanced and normally is computed by trial and error on thestandard tires in each size as made by the major rubber companies.

The invention contemplates that any method to determine the area oflaterally displaced weight in the tread or sidewall of the tire willmeet the objects of the invention. The simplest method appears to be asimple physical measurement such as with the tool defined hereinafter,but this measurement might be made at the factoryby x-ray, ultrasonic,or physical measurement 'a tire and which areas are thicker and heavier.It inplane 16 to other than a right angle with axis 14 and causingwobble, bearing wear, uneven tread wear, and an unsafe drivingcondition.

To substantially balance the tire of FIG. 1 dynamically without spinningfor almost all practical cases a weight W is secured to the tire support12 diametrically opposite to the area W. The center of mass of weight Wis at a distance R from axis 14 and at an axial distance A from centerplane 16. Therefore, substantial dynamic balance is achieved whenWI.R.AI. W.R.A. since and as the tire is spun on axis 14 all forcestending to tilt center plane 16 at other than right angles to axis 14are counter-balanced. This assumes, of course, that W is the onlyweighted area causing dynamic unbalance which is true in most practicaltire balancing situations. Naturally, it should be understood that ifweight W will cause a greater static unbalance when posi tioneddiametrically opposite area W it should then be placed on the oppositeside of the rim as indicated by cludes sensor means and 152 cooperatingwitha radiation source 154 such as, as x-ray for'example, to pulse'andtest sidewall and tread thickness and displacement from a central tireaxis. The source 154 produces an output drive signal to sensor means150'and means 152 produces an output signal which is representative ofthe tire sidewall and tread density, thickness and position from acentral rotating plane. This type of apparatus could also be ultrasonicactuated and include some mechanical means to determine lateral offset,with the x-ray or ultrasonic simply determining sidewall and treadthickness and/or density. Typical apparatus to effect the densitymeasurement is illustrated in US. Pat. No. 2,378,237.

Normally for a static balance of any pneumatic tire and rim assembly,one weight placed at the proper position on the rim will sufficeHowever, this single weight can be placed on either the inboard oroutboard side of the rim and still be equally effective for a staticbalance of the assembly. The method of this invention, however, requiresthat the static balancing weight be positioned at the point on the rimopposite to the laterally displaced area of the tire so as to at thesame time substantially correct a dynamic condition that a tire with alaterally displaced area will have during operation on a vehicle. Hence,if the tire has its heavy area on the outboard side, the weight will bepositioned on the outboard rim opposite the heavy area. If the tire hasits heavy area on the inboard side, the weight will be placed on theinboard rim opposite the heavy area.

I have found that better than a large number of the tires made today bythe major rubber companies and particularly the wide tread tires havelaterally displaced heavy areas normally caused by some slight cockingof the tire in the mold during cure. This method of balancing, based ondetermining the position of the laterally offset area, substantiallysolves both the dynamic and static problems at the same time with theuse of much less weight to achieve the balance.

With the tire in substantial dynamic balance as described the tire I isnext tested for static balance on the usual vertical spindle machine.Test weight 70 as seen in FIG. 2, may be utilized to determine theamount and position of the weight necessary for static balance. Anystatic out-of-balance may be compensated for by a pair of weights w andW one placed on one side of the tire support 12 and the other placed inaxial alignment on the other side of the tire support as shown. Theweights w and w are both at a distance r from the axis 14 and arediametrically opposite to the heavy side of the tire and its support.Placing the weights w and w equidistant from the center plane 16 doesnot upset the previously obtained substantial dynamic balance, but fullycompensates to obtain static balance even though dynamic compensatingweight W may have upset static balance. A single weight W3, indicated indotted lines, could be centrally positioned on the rim to take the placeof both weights w and W2.

Static balance is obtained, accordingly, when Turning now to theapparatus of the invention, a hublike portion 20 is generally providedhaving a skirt 22 which fits slidably down over the vertical spin dle ofa conventional spindle-type static balancer for a tire and rim support.A bubble 24 showing true horizontal may be provided at the top of thehub, although this is not necessary since the bubble in the balancerwill show through the open top of the hub. The purpose of the bubble onthe hub portion 20 itself is to help determine if a rim is out ofalignment, or if adding weight to compensate for dynamic out of balancechanges the static balance condition.

A plurality of arms 26 extend radially from the hub, preferably at 90spacing, the arms being calibrated in inches along their lengths. Rollermeans 28 are mounted on selected arms and include posts 30 locked inradially equal, but selected position, by set screws 32. A calibratedrod 34 is slidably received in each post 30 and is locked by set screw36 at selected height therein. Each rod 34 rotatably carries a ballbearing 38 at its lower and adapted to roll upon the bead retainingflange 40 of a tire support 42 (See FIG. 3) when the apparatus ismounted on the vertical spindle type tire balancer, as aforesaid. Notehowever, that the apparatus could have only one arm carrying both rollermeans 28 and gage means 46 so long as it carries a circular skirt 22 toslidably engage over the spindle.

In the preferred embodiment of the invention, gage means 46 are mountedon at least one arm 26a. The arms 26a are preferably longer than 26 arediametrically opposed to each other and situated midway between adjacentarms 26. Also arms 260 are curved at 26b to allow the arms to follow thecontour of a pneumatic tire. The gage means 46 includes a block 48secured in radially selected position with a set screw 50.

A calibrated rod 52 extends slidably through the block, and is eitherlocked in position in the block or given a selected sliding friction bya spring 54 secured to the block and adjustably forced into contact withthe rod by thumb screw 56, all as best seen in FIG. 4.

The rod 52 may be rounded at its lower end to engage with a selectedarea of the sidewall or tread of the tire, or may have a cup 58 securedthereto with set screw 60, the cup receiving chalk or crayon 62 held inplace by set screw 64.

In the operation of the apparatus described, with the hub 20, slidablyreceived over the vertical spindle of a tire balancer, the posts 38 areadjusted to bring rollers 38 into contact with the bead flange 40 (FIG.3) so that the entire apparatus of FIG. 2 can be rotated on the support42 of the tire and the support being tested. Normally, skirt 22 willcenter the apparatus with respect to the bead flange 40, but with-aminimum of two arms skirt 22 is not necessary if the rollers engageagainst the shoulder of the bead flange 40, as seen in FIG. 3. It shouldbe understood that substantial dynamic unbalance can be determinedwithout a static bubble balancer by the device of the invention rollingaround the bead seat of the tire support rim. For plastic or non-ferroussupports 42 the flange 40 may not have a shoulder, however, making useof the skirt 22 necessary for contral positioning of the apparatus withrespect to the spindle of a static balancer regardless of the number ofarms 26. Substantial dynamic balance has been achieved under controlledtesting conditions utilizing the device of the invention as describedabove.

Now at least one gage block 46 is adjusted to bring rod 52 over thesidewall or at the side of the tread of the tire under test and justinto contact therewith. Thumb nut 56 provides light friction on the rod52 allowing it to slide. The apparatus of FIG. 2 is rotated through atleast 180 and axially offset side areas of the tire are either markedwith chalk 62, or the distance of offset is measured by rod 52 slidingin block 48 or both. Once the distance of offset is known (such as areaW) the proper weight W can be selected and applied diametricallyopposite thereto to achieve dynamic balance. The amount of weight isdependent on the amount of axial offset, and the size andcharacteristics of the tire.

It is preferable to substantially dynamically balance both sides of thetire and its support in the manner described. In almost all instances,it will be found that the opposite sides of the tire are 180 out ofphase with respect to substantial dynamic balance so that the weightsnecessary to achieve substantial dynamic balance for both sides of thetire will statically cancel each other.

Next static balancing is effected as hereto fore set forth, the bubble24 facilitating this operation. However, to determine the amount ofweight necessary for static balance the invention contemplates thatsmall individual test weight 70, as seen in FIG. 2 of the drawings,might be slidably positioned by hand, on one of the arms 26a, with arm26a in the proper radial direction. The weights may be of variousincrements of weight, and one or more may be used and positioned in anyradial relation on arm 260 until by trial and error with one or moretest weights 70, the desired static balance is achieved-Normally, theweight or weights 70 are positioned in the same radial relation as thepermanent weights which will be attached to the rim.

Also, note that the gage block 46 can be adjusted so that rod 52 mightmeasure the radial out-or-round of the tread, as well as the axialdisplacement.

It should also be noted that the gage block 46 can be adjusted so thatrod 52 might measure the axial distance from the rim on both sides tothe point of attachmerit of the center support web of the rim definingthe plane of rotation of the tire, rim, wheel combination, so thatdynamic balance might be maintained where there is a difference in theseaxial distances, (especially true on the wide tread tire designsutilized today) by placing more weight when statically balancing withclip-on type weights on the side of the rim with the shorter distance tothe support web defining the plane of rotation of the tire, rim, wheelcombination. It has been found that the plane of rotation defined by theattachment point of the web normally carries the center of gravity ofthe rim and wheel when measured with the rim and wheel in a verticalplane. Therefore, it is usual in practicing the method of the inventionto properly distribute clip-on type weights during the static balance soas to not disturb the previously determined substantial dynamic balance.Normally this will require positioning of a greater amount of weight onthe outboard flange of the rim, than on the inner flange since theattachment point for the web of the rim is closer to the outboard flangethan the inboard flange in the usual wheel rim combination. I

FIG. 5 illustrates the arm arrangement of a modified embodiment of theinvention which though operating the same, is a little differentstructurally. Specifically, in this embodiment, a pair of rods 100'and102 are telescoped with relation to each other and held in a properlength position by appropriate cotter pin 104 to form each of the arms.A roller 106 is mounted to the end of rod 100 infixed position by anappropriate lock washer 108. The roller 106 rolls on the rim 110 in thesame manner as the roller 38 rolling on rim 40 as indicated in FIG. 3 ofthe drawings. In this embodiment, however, a test is made for theroundness or trueness of the rim itself, and this is made 1 rim 110, asillustrated. Hence, it should be understood that upon rotation of thetool, and the arm established by rods 100 and 102, the trueness orcircular roundness of the rim 110 will be measured by pin 114. Any majordeviations, or course, will either have to be corrected, or willindicate that the rim is unacceptable for high speed automobilepassenger tire operation.

FIG. 6 illustrates a plane view of the tool shown in FIG. 5, andillustrates four posts 102 spaced at 90 to each other and held to acenter hub 102a which is received around the spindle of a staticbalancing machine, as has been described above. However, FIG. 6 alsoillustrates a pair of arms 120 and 122 mounted in 180 relation to eachother on hub 102a. They are positioned at 45 relation between adjacentarms 102, and serve to measure lateral tread displacement for dynamicbalancing as described above. Each arm 120 and 122 mounts a plate 120aand 122a on which weight may be placed to determine the proper amount tostatically counterbalance the heavy area designated at 124. The plates120a and 122a operate in coordinator with arms 102 and pointers 126,128, and 132 mounted thereto. In effect, each arm 102 marks a point onthe rim in relation on each side of arms 120 and 122. The pointers 126and 128 mark a point on the rim in 60 relation on each side of arm 120while pointers 130 and 132 mark a point on the rim in 60 relation oneach side of arm 122.

The static balancing procedure with the tool is to place the hub 102aover the hub of a static balance device, and then to place either arm120 or 122 os it lies over the center of gravity of the heavy area. Thisis followed by placing weight onto the respective place on the oppositearm until static balance is achieved. Note that the plates 120a and 122aare marked with 0, 30, 45, and 60 designations. This means that weightspiled on the plate adjacent the respective designation, when the bubbleon a static balance device indicates proper balance, can be dividedexactly in half, with half mounted to the rim at the specific angulardesignation from the plate indicated. However, it should also beunderstood that the amount of weight necessary to counterbalance at 0can also be applied directly at the 60 indication by the respectivepointers 126 and 128, or 130 and 132 depending on which arm is utilizedwithout making the special determination adjacent the 60 indication onthe plate.

The optimum balance in a tire/wheel combination achieved by anequilateral balance such as the 120 relationship indicated in FIG. 6 ofthe drawings is shown in schematic form in FIG. 7. Specifically, thisfigure shows a relationship between a tire 130 and a rim 132 such thatthe tire has a radius R and the rim has a radius R/2. A four ounce heavyarea at 134 will require 8 ounces balancing compensation weight atpoints 136 and 138, respectively, on the rim at 120 spaced relationshipfrom the radial position of the 4 ounce out-ofbalance area 134. Thisgenerates an equilateral triangle illustrated by a solid line 140 andmeans that equal thrust will prevail throughout the entire tire/rimcombination due to centrifugal force during rotational operation of thetire. This uniform distribution of weight means that'exactly 4 ounces ofthrust will be present at each of the 60 points marked around theperiphery of the tire during rotational operation thereof. This can verygreatly eliminate rough ride due to unequal radial or circumferentialforce distributions in the tire because of the unequal balance aroundthe entire tire combination that may be present if a single lumpedweight is utilized opposite the 4 ounce heavy area 124.

It is also possible utilizing the tool shown in FIG. 6 of the drawingsto determine whether the heavy area 124 is spread over a long arcuatesection of the tire, which is normally the case because of shifting ofthe tire during molding or whether the heavy area 124 is localized dueto some local condition such as a radial lap splice, or some heavylocalized condition within the rubber compounding itself. The techniqueto determine this relationsip is to simply determine the exact amount ofweight necessary to counterblance the heavy area 124 on both plates kand 122b. The amount of weight necessary to counterbalance on plate 120bwill be the same regardless of whether the heavy area is distributed orlocalized at 124. However, on plate 122b, it will be found that lessweight is necessary to counterbalance at the 45 points shown by arms 122and 1220 when the heavy area 124 is spread over a longer arcu-. atedistance than the heavy area is localized. A table can easily be made upto allow the operator of the tool to utilize this determination as tothe extent of the heavy area being spread or localized, for it can be ofgreat value to the factory to enhance quality control procedures. Theproof of this method is quite easily accomplished by simply placingweights on the tire during use of such tool in either a localized heavyarea or a spread heavy area, and actually counterbalancing on the 45relationship with arms 122 and 122a, to show that different amounts ofweight are necessary to counterbalance at the points designated by arms122 and 122a, even though exactly the same amount of weight on plate122b will indicate the counterbalance with the weight localized at 124or spread out over a long arcuate distance.

Hence, it should be understood that the tool of the invention incombination with the balancing method described achieves the followingimproved features:

1. Can determine static balance on even an improp-' erly operatingstatic balance machine by use of the circular level placed over thecenter hub.

2. Can determine a warped rim by the four equal arms rolling around therim. If the rim is warped, the arms will not contact equally and thewarp can be detected.

3. Can determine out of round rims by the pins 14 extending down fromthe arms. Either one or more pins may be utilized on one or more of thearms.

4. The device can determine if the tire is out of balance over a longcrescent area or a condensed area by means of the arms 102 and the 45designation on either plate 120a or 1220.

5. The device locates the weight to the correct position for equilateralbalance and equal centrifugal force thrust in the rotating tire bydetermining the correct amount of the weight and the position thereof bymeans of arms 122 and plates a and 122a.

6. The device locates dynamic unbalance in the majority of tire caseswhere lateral disproportionates may exist in the tread or sidewall of atire and corrects for these unbalances with a properly positionedweight.

7. The device determines out-of-roundness in tires by an appropriateadaptor to one of the measuring arms.

While in accordance with the patent statutes only one best knownembodiment of the invention has been illustrated and described indetail, it is to be particularly understood that the invention is notlimited thereto or thereby but that the inventive scope is defined inthe appended claims.

What is claimed is:

1. That method of substantially dynamically and statically balancing acombination pneumatic tire and its support assembly having a laterallyoffset heavy area which includes the sequential steps of a. directing aradiation waveform through the lateral side walls and tread area of thetire to determine the area of maximum thickness and density; and

b. mounting the assembly on a static tire balance apparatus andpositioning compensating weight on the supportassembly on the same sideof the tire and support assembly as the determined area at a pointopposite such area so as to complete the static balance of the assemblyas measured by the balancing apparatus, and also help compensate for thedynamic unbalance.

1. That method of substantially dynamically and statically balancing acombination pneumatic tire and its support assembly having a laterallyoffset heavy area which includes the sequential steps of a. directing aradiation waveform through the lateral side walls and tread area of thetire to determine the area of maximum thickness and density; and b.mounting the assembly on a static tire balance apparatus and positioningcompensating weight on the support assembly on the same side of the tireand support assembly as the determined area at a point opposite sucharea so as to complete the static balance of the assembly as measured bythe balancing apparatus, and also help compensate for the dynamicunbalance.